Bluestone Mortgages, part of the Bluestone Group, was established in 2014 and specialises in owner-occupied mortgages.
Shawbrook and Bluestone Mortgages first established a platform lending arrangement in 2017 and, according to Shawbrook, have maintained a successful relationship since then.
The acquisition is expected to be completed in the second quarter of this year.
Shawbrook group chief executive Marcelino Castrillo said by bringing the two organisations together, they hope to use their combined capabilities and scale to “offer an even stronger proposition to UK homeowners”.
“Driven by increasing numbers of people choosing to work for themselves or in sectors where incomes are complex, we anticipate significant long-term growth in the specialist mortgage market.
"With both Bluestone Mortgages and The Mortgage Lender brands combined with Shawbrook's strong and stable balance sheet, the group is very well placed to consistently meet this growing demand,” Castrillo said.
Bluestone Mortgages chief executive, Steve Seal added: “We have exciting growth plans and the support available from Shawbrook will help to accelerate these, enabling BML to provide innovative lending solutions to the growing number of customers who will need the support of a specialist mortgage lender."
Australian-based Bluestone Mortgages launched in the UK in 2015.
It announced its first profit after tax during the Covid pandemic in 2021.